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Modifying a Conventional UASB Reactor to an Integrated UASB-g
Digester System for Sewage Pre-Treatment in Mountain Areas at Low
Temperatures (15 °CTemperatures (15 °C
Nidal Mahmoud, Grietje Zeeman, Jules B. van Lier, Gatze LettingaInstitute of Environmental and Water Studies,Institute of Environmental and Water Studies,Institute of Environmental and Water Studies,Institute of Environmental and Water Studies,
BirzeitBirzeit [email protected]
Ecological Sanitation Training CourseSWITCH PROJECT
IEWS, Birzeit University, 25-27 January 2011
Modifying a Conventional UASB Reactor to anModifying a Conventional UASB Reactor to an Integrated UASB-Digester System for Sewage
Pre-Treatment in Mountain Areas at Low T t (15 °C)Temperatures (15 °C)
Nid l M h d G i tj Z J l B Li G tNidal Mahmoud, Grietje Zeeman, Jules B. van Lier, Gatze Lettinga
Sub-Department of Environmental Technology W i U i it Th N th l dWageningen University, The Netherlands
Water studies Institute,Birzeit University, Palestine
1st IWA International Workshop Anaerobic Digestion in Mountain Area (& isolated
rural zones)
Wastewater f lfacilities in Palestine
Ramallah WWTP: primary clarifier + ponds
Open conveyance & drains Al-Bireh WWTP: Oxidation Ditch
Wastewater characteristics in PalestineWastewater characteristics in Palestine
Vulnerable society with very limited water resources andlimited water resources and virtually no treatment
Decentralised treatment willDecentralised treatment will play an important role in the Palestinian water sector
biogas use
Application of full scale Anaerobic WWTP in tropical areas biogas usep
influent effluentU A S B
Post treatment
screening grit chamber
U A S B
- polishing pond- Trickling filterg- RBC- activated sludge- etc.
sludge drying bedreusewater
l d sludge drying bedsludgebiogas
UASB Overall Results “Sewage treatment”
COD Removal:………………. 70 - 80% BOD Removal: ………………. 75 - 85%SS Removal: 70 80%
Average Results Latin America SS Removal: …………………. 70 - 80%
Pathogen Removal: - Coliforms: 70 - 90%
Latin America and India:(COD < 500/600 mg/l)
- Helminth eggs: “up to 100%”
14.000 m3/d UASB Mirzapur 12.000 m3/d UASB BucaramangaIndia Colombia
UASB: options for decentralised sewage treatmentUASB: options for decentralised sewage treatment
Campina Grande, Brasil Odemira, Portugal
Masterplan of Recife metropolitan area: decentralised approach(Florencio et al., 2001)
Overall project goal:Overall project goal: Assessment feasibility of anaerobic sewage treatment in the mountain areas of Palestinetreatment in the mountain areas of Palestine
Specific goalsA t l l h t i ti ( t k )• Assessment local sewage characteristics (not known)
• Validation of the technical feasibility of a UASB-digester systemdigester system
• Optimising the digester design
I. Wastewater Characteristics of Ramallah City, Al-Bireh City and Al-Jalazoon refugee camp
Parameters Ramallah Al-Bireh Al-Jalazoon
Bireh City and Al Jalazoon refugee camp
Highest altitude: 1000 m!COD Total 2180 1586 1489
Suspended 1096 919 725 Colloidal 323 274 327
Dissolved 761 393 438VFA as COD 187 160 123 SO4
2- as SO42- 975 138 213
TSS 729 736 630TSS 729 736 630VSS 584 617 480 pH 7.45 7.26 7.31 T Summer 30 9 25 8 23 4Tww Summer 30.9 25.8 23.4
Winter 13 Tamb. Summer 27
Winter 13 8 Winter 13.8Colour Reddish to black Medium brown Light brown
‘Multiplicate’ time interval composite samplesMultiplicate time-interval composite samples
Impact of Low Temperatures:
At low temperatures (< 15ºC) and/or strong temperature fluctuations between summer (25ºC) and winter (15ºC), the i l t UASB t d i d id tisingle step UASB reactor design needs reconsideration:
Limited HydrolysisLimited Hydrolysis
Accumulation of particulate
High SS
Accumulation of particulate organic matter Limited
hydrolysis
Deterioration of the reactor performanceLong retention
Low removal efficiency
gtime
Required SRT for Hydrolysis in Reactor
160
180
Required SRT for Hydrolysis in Reactor
120
140
160
e [d
ays] Conventional UASB:
HRT 22-24 hrs!!
80
100
ed s
ludg
e
40
60
r st
abili
ze
0
20
SRT
for
10 15 20 25 30 35 40 45
Temperature [°C]
Amended process designs for low temperature sewage treatment
Stable reactor performance by separating: 1 R l d di ti f d d lid
low temperature sewage treatment
1. Removal and digestion of suspended solids 2. Conversion (bio-methanation) of colloidal and soluble COD
Various set-ups has been proposed:
1. HUSB reactor followed by UASB2. HUSB reactor followed by EGSB3. AF followed by AH system3. AF followed by AH system4. Two-stage UASB system
1 7AF reactor AH reactorTarek Elmitwalli (2001)
UASB - Digester system
Gas metersGas holder
Effluent
UASBDigester Nidal Mahmoud
(PhD thesis 2002)
g W
ater
(PhD thesis, 2002)
Hea
ting
InfluentExcess sludge
II Digester optimisationII. Digester optimisationSubstrate: primary sludge diluted to 20 g TS/l
2 x 8 CSTRs (duplicate):SRT: 10, 15, 20, and 30 daysTemp.: 25 and 35 ºC20 g TS/l.
outlet
Temp.: 25 and 35 C
T = 25°C Expressed as percentage of influent COD inletT = 25°C Expressed as percentage of influent COD
SRT in days: 0 10 15 20 30
Hydrolysis 10 24 41 41 42
gas bag
y y
Acidogenesis 6 22 39 41 42
Methanogenesis 0 11 39 41 42
T = 35°C Expressed as percentage of influent COD
CSTR digesterSRT in days: 0 10 15 20 30
Hydrolysis 10 41 45 47 49
A id i 6 41 45 47 49Acidogenesis 6 41 45 47 49
Methanogenesis 0 41 45 47 49
II Digester optimisationII. Digester optimisation
Overall Results:Al l di i f i b h d outlet
inlet
Almost complete digestion of proteins, carbohydrates and lipids within 15 and 10 days at 25 and 35 °C, respectively.
gasHydrolysis constant (kh), fraction hydrolyzed (fh)
gas bag
CSTR digesterCSTR digester
III. The UASB reactor and UASB-Digester system
HRT: 20 d
HRT: 6hrs HRT: 6hrsTemp : 15ºC
HRT: 20 dTemp.: 35ºCMix.: 8 rpm
Temp.: 15ºC Temp.: 15ºC
Single stage UASB pilot plant (140 l)
UASB-Digester pilot plant (140 l + 106 l)
Period 1: 81 days operation
( )
Period 2: 83 days operation
Substrate: dilute sewage from Bennekom village, The Netherlands,COD: 500 – 750 mg/l
Results UASB - Digester systemUASB t t 15 ºC !!
Effluent concentrations
UASB reactor temp.: 15 ºC !!
Effluent concentration (mg/L)Reactor CODt CODss CODcol CODdis VFA-CODUASB 390 100 128 162 80
(62) (36) (19) (47) (40)UASB-Digester 151 32 68 50 3
(34) (24) (17) (10) (3)
Removal efficienciesRemoval efficiency (%)Reactor CODt CODss CODcol CODdis VFA-COD
UASB 44 73 3 5 -8(9) (14) (46) (17) (42)(9) (14) (46) (17) (42)
UASB-Digester 66 87 44 30 95(6) (5) (15) (36) (8)
COD Removal efficiency in comparison with UASB’s applied in tropical countries
UASB-Digester
Sao Paulo -Brazil
Bucaramanga -Columbia
Kanpur - India(Draaijer et alDigester
(This study)Brazil(Vieira, 1988)
Columbia(Schellinkhout et al., 1988)
(Draaijer et al.,1992)
HRT (hr) 6 4.7 - 9 5 6Temp (C) 15 21 - 25 23 - 27 20 - 30Temp ( C) 15 21 25 23 27 20 30COD (%) 66 (6) 70 66 62 - 70
Th UASB Di t tThe UASB-Digester system: 3.5 times less sludge than a parallel operating UASB reactor !!UASB: 0.77 g sludge-COD/g CODrem., 0.09 Nm3 CH4/Kg CODrem.g g g rem., 4 g rem.UASB-Digester: 0.21 g sludge-COD/g CODrem., 0.17 Nm3 CH4/Kg CODrem.
30
40
rati
on TS (UASB-Digester) VS (UASB-Digester)
10
20ds
con
cent
r(g
/L)
010 29 39 49 63 69 79 90 100
Sl d b d h i ht (%)
Soli
d
Sludge bed height (%)
UASB-Digester70
%)
60
65
VS/
TS (%
5510 29 39 49 63 69 79 90 100
sludge bed height (%)
Sludge profile in UASB-unit of UASB-Digester system as VS and TS (a) and VS/TS ratio (b) along the sludge bed height expressed as percentagesand VS/TS ratio (b) along the sludge bed height expressed as percentages of the total bed height. 0% = reactor bottom; 100% = 1.90 m.
Full scale calculations for Palestine:O ti i i l UASB CSTR itOptimising volumes UASB + CSTR unit
Model calculations using:g- obtained kinetic constants- Palestinian sewage characteristics
UASB: 0.25 m3/m3 sewageCSTR: 0.107 m3/m3 sewage
(40-45% of UASB reactor volume)
Based on:Based on:- UASB: 6 hrs HRT- CSTR-temp.: 35°C
SRT (CSTR) 15 d- SRT (CSTR): 15 days- Sludge recycling from bottom of UASB: 22 g VS/l
Conclusions 1
Sewage in Palestine is of high strength (COD: 1500-2200 mg/l, TSS: 650-750 mg/l) and low temperatures (15 ºC) during winter time
Conventional single stage UASB reactors in Palestine require HRTs approaching 1 day (3 x the value of tropical applications) pp g y ( p pp )
E t i t bili ti f i l d i th l d CSTRExtensive stabilisation of primary sludge in the coupled CSTRs occurs within the first 15 and 10 days SRT at 25 and 35 ºC, respectivelyp y
Conclusions 2
The enhancement of methanogenic conditions in UASB reactor, g ,improves both physical removal and hydrolysis of solids
The UASB-Digester system is a technically feasible alternative for h h h ( ) d hhigh-strength sewage (pre) treatment at 15 ºC, reducing the required HRT to 8 hrs (similar to tropical applications)
160017001800
35
40stage 2 stage 3stage 1
1200130014001500
30
900100011001200
(mg/
L)
20
25
atur
e (°
C)
600700800900
CO
Dto
t
15
20
Tem
pera
300400500600
10Influent COD totalEffl t UASB t
0100200
0
5Effluent UASB reactorTemperature
0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510
time (days)
Influent, effluent and air temperature during the anaerobic treatment of domestic sewage from Al Bireh City/Palestine in a one stage UASB reactor (Stage 1) and a modified UASB reactor to a UASB-Digester system through sludge re-circulation from the digester to the UASB reactor (Stage 2 and 3)
0 50 100 150 200 250 300 350 400 450 500
time (days)
90.000
100.000
30
350 50 100 150 200 250 300 350 400 450 500
stage 1 stage 2 stage 3
70.000
80.000
25
30
C)
50.000
60.000
TS
(g/L
)
15
20
erat
ure
(°CTS tap 1
TS tap 2TS tap 3T
30.000
40.000T
10
15
Tem
pTemp
0 000
10.000
20.000
0
5
0.0000 21 32 62 93 130 193 266 289 352 377 396 424 446 462 483
time (days)
0
Sludge profile of a one stage UASB reactor (Stage 1) and a UASB reactor of a UASB-Digester system (Stage 2 and 3) in terms of TS and ambient air temperature during the anaerobic treatment of domestic sewage from Al Bireh City/Palestine